Color picture tube beam convergence apparatus

ABSTRACT

For a color picture tube having a plurality of electron beams emanating from the neck of the tube in a nominally common plane two pairs of diametrically magnetized ceramic ferrite discs mounted on opposite sides of the tube neck are rotatable to vary the strength and orientation of their respectively produced magnetic fields, thereby converging the beams at the screen of the tube.

United States Patent Mirsch Oct. 24, 1972 [54] COLOR PICTURE TUBE BEAM3,553,523 1/1971 Budd ..313/77 X CONVERGENCE APPARATUS 3,453,472 7/1969Burdick ..3l3/77 3,290,532 12/1966 Lemke et a1. ..335/212 X U2]2,854,598 9/1958 Baermann ..313/77 [73] Assignee: RCA Corporation2,854,607 9/1958 Niklas et a1. ..3 13/77 UX [22] Filed: 1971 PrimaryExaminer-George Harris [21] Appl. No.: 112,348 Attorney-E. M. Whitacre 57 ABSTRACT [52] U.S. Cl.....' ..335/2l2, 313/77 I 51] Int. Cl. .1101:1/00 a 991m Picture tube having a plurality of electron [58 Field ofSearch ..335/210, 212, 213; 313/77, beams emanating from the neck of thetube in 313/70 315/27 nominally common plane two pairs of diametricallyv magnetized ceramic ferrite discs mounted on opposite Re "new Citedsides of the tube neck are rotatable to vary the [56] e strength andorientation of their respectively produced UNITED STATES PATENTSmagnetic fields, thereby converging the beams at the f th 2,887,5985/1959 Benway ..313/70 0 screen 0 e tube 3,430,099 2/1969 Ashley..315/27 10 Claims, 7 Drawing Figures PATENTEDMT 24 I912 INVENTOR. 101mWMirscb ATTORNEY 1 COLOR PICTURE TUBE BEAM CONVERGENCE APPARATUSBACKGROUND OF THE INVENTION In the operation of a multi-beam colorpicture tube it is necessary that the plurality of electron beams enterthe raster-producing deflection region in such positions relative to oneanother that they converge at the viewingscreen. It is not practicallyfeasible, in the fabrication of such a tube, to position thebeam-producing electron guns with such precision that the beams will beautomatically converged at the screen. Also, the deflection yoke,particularly onehaving toroidal windings, produces stray fields thatadversely affect the beams, such as by defocusing them. In order tominimize such adverse effects relatively high permeability structuressuch as I internal convergence pole pieces, commonly used in othermulti-beam color picture tubes, can be eliminated, thereby reducing thecoupling of stray deflection fields into the predeflection region of thebeams. It is still necessary, however, to influence the beams so thatthey will converge at the screen of the tube.

Previously, constant strength permanent magnets have been used toachieve the desired static beam convergence. The necessary effect of theproduced magnetic fields upon the beams has been achieved by vary ingthe spacing between the magnets and their associated beams. Suchapparatus has two principal disadvantages in a tube with no internalpole pieces; one is that only one linear beam movement is possible; theother is that fringe fields undesirably spray out from such magnets asthey are moved away from the beams, thereby adversely affecting thebeams in more sensitive areas.

SUMMARY OF THE INVENTION The beam convergence apparatus of thisinvention has particular utility with a color picture tube of thesocalled in-line electron beam type in which a plurality of electronbeams emanate from the neck of the tube nominally in a common plane. Theconvergence apparatus comprises two low permeability permanent magnetstructures disposed respectively on opposite sides of the tube neck.These magnet structures produce respective fields by which to influencethe electron beams appropriately to effect their substantial convergenceat the viewing screen of the tube. In order that the producedfieldseffect the desired influence, the magnet, structures are providedwith means for suitably adjusting the strength and the orientation ofthe produced fields. In a particular embodiment of the invention each ofthe magnet structures includes a pair of diametrically magnetizedceramic ferrite discs coaxially disposed relative to one another. Thediscs are rotatable relative to one another to adjust the strength ofthe produced field. Also, each of the structures is rotatable as a unitabout an axis parallel to the longitudinal axis of the tube to adjustthe orientation of the produced field. For a more specific disclosure ofthe invention reference may be had to the following description of anillustrative embodiment thereof which is given in conjunction with theaccompanying drawing, of which:

FIG. 1 is a diagrammatic top view of a color picture tube having threein-line electron guns and showing the general positions of the beamconvergence apparatus of this invention in relation to other adjunctsused in the operation of the tube;

FIG. 2 is a fragmentary sectional view taken on the line 2-2 of FIG. 1and showing the rear end view of the beam convergence apparatus;

FIG. 3 is an enlarged view of one of the permanent magnet structures ofthe beam convergence apparatus;

FIG. 4 is an exploded view of the magnet structure of FIG. 3 and showingthe relationship of the components of the magnet structure;

FIG. 5 is a sectional view taken on the line 5-5 of FIG. 4 and showingthe details ofone of the magnetretaining collars of the apparatus;

FIG. 6 is a sectional view taken on the line 6--6 of FIG. 4 and showingthe configuration and magnetization of one of the magnet components ofthe beam convergence apparatus; and

FIG. 7 is a diagrammatic representation of the operation of the beamconvergence apparatus of the invention.

DESCRIPTION OF THE INVENTION In FIG. 1- the three beam shadow mask typeof color picture tube 11, with whichthe beam convergence apparatus ofthe invention is used, has a relatively large flared front section 12and a relatively small cylindrical neck section 13. The face plate 14 atthe front of the flared section 12 has formed on its rear surface afluorescent screen 15 comprising a multiplicity of triads of phosphordots which are excitable by respective electron beams to produce lightof three difierent colors such as red, green and blue. A shadow mask 16having a plurality of apertures aligned with the triads of phosphor dotsof the screen 15 is mounted in back of the screen and functions, incooperation with other elements of the tube, to direct the threeelectron beams to their respective phosphor dots. Three electron guns17, 18 and 19 are mounted in the neck section 13 of the picture tube 11.to produce, when suitably energized, the three electron beams forexcitation of the screen 15. The electron guns 17, 18 and 19 are locatedin a common horizontal plane in a so-called in-line arrangement.

A deflection yoke 21 is mounted externally of the tube 11 in the regionin which the neck section 13 merges with the flared section 12. The beamconvergence apparatus 22 comprising this invention is located onopposite sides of the neck section 13 immediately to the rear of thedeflection yoke 21. A color purity device 23 is mounted still further tothe rear on the neck section 13 of the tube 11. The color picture tube11 and the described adjuncts, except for the convergence apparatus 22,are generally known and used and hence need no additional'description orexplanation.

The general FIG. 2 rear view of the convergence apparatus 22 shows itstwo magnet structures 24 and 25 on opposite sides of the picutre tubeneck 13 and centered, as an example, in the same horizontal plane withthe three electron beam-producing guns l7, l8 and 19.

The magnet structures 24 and 25 are mounted, in a manner to be describedpresently, in respective halves 26a and 26b of a non-magnetic plate 26which effectively encircles the tube neck 13. Because it is desirable toposition the convergence apparatus, including the magnet structures 24and 25, immediately to the rear of the deflection yoke 21 the plate 26may also serve as the terminal board for the yoke windings. The twomounting half-plates 26a and 26b may be secured to one another by anysuitable means such as a pair of spring clips 27.

In FIG. 3 an assembled profile view (enlarged to approximately fourtimes actual size) of one of the magnet structures 24 is shown as it ismounted on the halfplate 260. Both of the half-plates 26a and 26b areconstructed of non-magnetic material such as lucite for example.Two'magnet discs (not shown in this figure) are supported withinrespective non-magnetic annular retaining collars 28 and 29 and arecoaxially mounted on a non-magnetic flanged spindle 31 which extendsthrough the half-plate 26a.

In the FIG. 4 exploded view of the magnet structure 24 of FIG. 3 theretaining collars 28 and 29 have centrally disposedholes 32 and 33,respectively, to snugly receive ceramic magnet discs 34 and 35. Thethicknesses of the magnet discs 34 and 35 are substantially the same asthose of their respective retaining collars 28 and 29 so that the facesof the magnet discs effectively abut one another when assembled as shownin FIG. 3. The magnet discs 34 and 35 have centrally disposed holes 36and 37 respectively for snug mounting on the spindle 31. With the magnetdiscs 34 and 35 respectively supported within the holes 32 and 33 of theretaining collars 28 and 29, the spindle 31 extends through the discholes 36 and 37 into a hole 38 in the half-plate 26a. The spindle 31 hasa flange 39 so as to securely mount the components of the magnetstructure 24 on the half-plate 26a as shown in the assembly on FIG. 3.The retaining collars 28 and 29 and their respectively supported magnetdiscs 34 and 35 are adjustably rotatable about an axis 40 which isparallel to the longitudinal axis of the picture tube 11. It will beunderstood that the magnet structure 25 of FIG. 2 is similarlyconstructed.

The FIG. view of the retaining collar 29 shows the peripheral edge ofits flange portion to be notched such as by gear teeth 41. The purposeof the gear teeth 41 is to facilitate manipulative rotation of thecollar and its supported magnet disc 35 about the spindle 31.

Each of the magnet discs, such as the disc 35 of FIG. 6, may be formedof a ceramic material such as plastic barium ferrite. Such a materialhas a relatively low permeablility and, when diametrically magnetized asindicated in this figure, is more strongly magnetized on one face thanon the other. The mounting of the magnet disc 35 of FIG. 6 in theretaining collar 29 of FIG. 5 should be such that the strongermagnetized face is away from the notched flange 41 of the retainingcollar. The magnet disc 34 should be similarly mounted in the collar 29.In this way the stronger magnetized faces of the magnet discs 34 and 35will abut one another when the structure is assembled as indicated inFIGS. 3 and 4, thereby producing an effective field for electron beamconvergence.

In operating of the electron beam convergence apparatus of thisinvention the strength of the resultant beam-controlling field isadjusted by manipulation of the notched peripheral edges, such as theedge 41 of the collar 29, of the two retaining collars 28 and 29relative to one another. For example, when the N and S poles of themagnet discs 34 and 35 are aligned respectively with one another, theresultant field has maximum strength. A minimum strength field isproduced by aligning the N pole of one magnet disc with the S pole ofthe other disc. Field strengths of intermediate values are produced byrelative positions of the magnet discs 34 and 35 intermediate of the twodescribed extreme positions. The orientation of the resultant field isdetermined by the angular positioning of the mutually adjusted magnetdiscs 34 and 35 relative to the supporting spindle 31.

' A graphical example of the manner in which the convergence apparatusof this invention enables the accomplishment of the desired result isdepicted in FIG. 7. It will be assumed that the desired convergence ofthe electron beams at the viewing screen can be achieved by positioningthe beams symmetrically about the longitudinal tube axis in a commonhorizontal plane indicated by the broken line 42. It will also beassumed that the beams issue from their respective electron guns in therelative positions represented by the squares 43, 44 and 45. In thisassumed example the middle beam is in its desired position substantiallyat the center of the tube neck 13 and in the common plane 42 asindicated by the circle 44'. The left-hand beam position 43, however, isabove the common plane 42 and closer to the center of the tube neck 13than it should be for effective convergence with the middle beam at theviewing screen. Also, the right-hand beam position 45 is below thecommon plane 42 and farther from the tube neck center than it should befor convergence with the middle beam.

The rotation of the complete magnet structures 24 and 25 about therespective axes 40 and 40' causes the associated electron beams to bemoved in substantially circular patterns. The magnitude of each circularpattern is determined by the rotational adjustment of the two componentmagnet discs (such as the discs 34 and 35 of FIG. 4) relative to oneanother. The left-hand beam, for example, may be positioned anywhere onthe circular pattern 46 by a suitable rotational adjustment of themagnet structure 24 about the axis 40. Such latter adjustment determinesthe particular orinentation of the produced field and, thus, controlsthe direction in which the beam is moved to a selected position on thecircular pattern 46. In the case of the left-hand beam, it may be movedfrom the position 43 to the position 43' efiectively along the line 47.The length of the line is determined by the strength of the producedfield which is a function of the relative rotational adjustments of thecomponent magnet discs of the structure 24. The angular relationship ofthe line 47 to the common plane 42 is determined by the orientation ofthe produced field which is selected by the rotational adjustment of themagnet structure 24 about the axis 40.

In a similar manner the right-hand beam may be effectively moved fromposition 45 to position 45 In this case it is necessary to rotationallyadjust the component magnet discs of the structure 25 to produce asomewhat stronger field than that produced by the structure 24, therebyto determine a larger circular pattern 48 than the pattern 46. Also,this stronger field must be oriented by a rotational adjustment of themagnet structure 25 about the axis 40' so that the diametral line 49,representing the effective path of beam movement, is angularly relatedto the common plane 42 in a way to cause the beam to be moved fromposition 45 to position 45.

Because of the inherently close spacing of the electron beams within theneck 13 of the picture tube 11 permeability structures, such as internalpole pieces, 1

from thevicinity of the electron beams insures an unobjectionableminimum, if any, coupling of the field produced by the deflection yoke21 into the predeflection region occupied bythe beams. Also, because themagnet structures 24 and 25 remain always at the same distance from theelectron beams, the fields produced thereby do not spray out toadversely affect the beams in more sensitive areas. While the magnetstructures are shown herein mounted in the common plane of the beams,they are not necessarily limited to such positions because of the factthat they operate in such a manner that coordinate X and Y motions ofthe beams are produced. Hence, the angular positioning about thelongitudinal axis of the picture tube 11 of the magnet structures 24 and25 is not critical.

What is claimed is: l

1. The combination comprising:

a tri-beam color kinescope having a screen for display of a colorpicture in response to the scanning thereof by a plurality of electronbeams in a succession of substantially parallel line sweeps, and havinga cylindrical neck enclosing a trio of in-line beam paths, a central oneof said in-line beam paths substantially coinciding with thelongitudinal axis of said neck with the remaining outer ones of saidin-line beam paths being substantially symmetrically disposed onopposite sides of said axis, and with all of said in-line beam pathstraversing a region of the interior of said neck which is free ofreadily magnetizable structures;

means for shifting one of said outer beam paths in a selectable one of aplurality of directions inclusive of directions parallel to,perpendicular to, and diagonal to the direction of said line sweeps,said shifting means comprising a first adjustable permanent magnetmeans, mounted on the exterior of said tube neck for positioning on oneside of said tube neck region in a first location closely adjacent oneof said outer beam paths, for producing a magnetic field intersectingwith primary influence said one of said outer beams with a selectableone of a plurality of directions inclusive of directions parallel to,perpendicular to, and diagonal to the direction of said line sweeps; and

additional means for shifting the other of said outer beam paths in aselectable one of a plurality of directions inclusive of directionsparallel to, perpendicular to, and diagonal to the direction of saidline sweeps; said additional shifting means comprising second adjustablepermanent magnet means, mounted on the exterior of said tube neck forpositioning on the side of said tube neck region opposite to said oneside in a secondv location closely adjacent said other of said outerbeam paths, for producing a magnetic field intersecting with primaryinfluence said other of said outer beams with a selectable one of aplurality of directions inclusive of directions parallel to,perpendicular to, and diagonal to the direction of said line sweeps;

and wherein each of said first and second permanent magnet fieldproducing means is independently adjustable.

2. Beam convergence apparatus for a color picture tube having aplurality of electron beams emanating fromthe neck of said tube in anominally common plane and subject to passage toward the screen of saidtube through a region of said neck free of the presence of internalmagnetizable pole piece structures, said apparatus comprising:

two permanent magnet structures mounted for respective positioning onopposite sides of said tube neck region for producing respective fieldsto primarily influence respectively different ones of said plurality ofbeams; and

means for adjusting the strength and orientation of the field producedby each of said respective mag netic structures, such field orientationadjustments enabling shift of the associated beam in a selectable one ofa plurality of directions inclusive of a direction parallel to adiagonal of said screen; and wherein:

each of said magnet structures includes a pair of magnetized discs oflow permeability material coaxially disposed relative to one another ina mounting therefor,

' each disc being magnetized on a diameter, and

said discs being rotatable relative to one another to vary the strengthof the produced magnetic field.

3. Beam convergence apparatus as defined in claim 2, wherein:

each of said magnet structures is rotatable about an axis that isparallel to the longitudinal axis of said tube to vary the orientationof the produced magnetic field.

4. Beam convergence apparatus as defined in claim 3, wherein:

said magnetized discs are ceramic of barium ferrite material with themagnetization being stronger on one face thereof than on the other, and

each of said magnet structures being assembled with the strongermagnetized faces of said respective discs abutting one another.

5. Beam convergence apparatus as defined in claim 4, wherein:

said disc mounting includes a non-magnetic spindle,

and

said discs are provided with central transverse holes to snugly fit oversaid spindle.

6. Beam convergence apparatus as defined in claim 5, wherein:

said disc mounting also includes a non-magnetic annular retaining collarhaving an inside diameter so related to the outside diameter of saiddisc that the disc is firmly secured within the collar.

7. Beam convergence apparatus as defined in claim 6, wherein:

said disc mounting further includes a non-magnetic plate disposed aroundthe neck of said tube normal to the longitudinal tube axis, andtransverse holes through said plate on opposite sides of said tube neckin said common plane to receive said respective disc-supportingspindles. 8. Beam convergence apparatus as defined in claim 7, wherein:

each of said disc-supporting spindles has a flange at one end toconstrain said disc-retaining collars to rotary movements between saidflange and said plate. I 9. Beam convergence apparatus as defined inclaim 8, wherein:

said disc-retaining collars have notched peripheral edges by which toeffect said field strength and orientation varying rotations of saiddiscs. 10. In combination with a multibeam shadow-mask color kinescopehaving a neck enclosing a plurality of in-line beam sources, said beamspassing from said sources toward the screen of said kinescope through aregion of said neck free of the presence of magnetizable structures,apparatus comprising:

a first pair of magnetized discs of low material; a second pair ofmagnetized discs of low material; an apertured mount of non-magnetizablematerial for said first and second disc pairs, said tube neck beingreceived within the aperture of said the mount, and said mount beingpositioned along the neck axis so as to encircle said structure-freeregion of said neck; and means for rotatably supporting each of saidpair of discs on said mount in respective diametrically opposedpositions spaced from said mount aperture, the discs of each pair beingcoaxially disposed and subject to individual rotation about an axissubstantially parallel to the axis of said neck.

permeability permability

1. The combination comprising: a tri-beam color kinescope having ascreen for display of a color picture in response to the scanningthereof bY a plurality of electron beams in a succession ofsubstantially parallel line sweeps, and having a cylindrical neckenclosing a trio of in-line beam paths, a central one of said in-linebeam paths substantially coinciding with the longitudinal axis of saidneck with the remaining outer ones of said in-line beam paths beingsubstantially symmetrically disposed on opposite sides of said axis, andwith all of said in-line beam paths traversing a region of the interiorof said neck which is free of readily magnetizable structures; means forshifting one of said outer beam paths in a selectable one of a pluralityof directions inclusive of directions parallel to, perpendicular to, anddiagonal to the direction of said line sweeps, said shifting meanscomprising a first adjustable permanent magnet means, mounted on theexterior of said tube neck for positioning on one side of said tube neckregion in a first location closely adjacent one of said outer beampaths, for producing a magnetic field intersecting with primaryinfluence said one of said outer beams with a selectable one of aplurality of directions inclusive of directions parallel to,perpendicular to, and diagonal to the direction of said line sweeps; andadditional means for shifting the other of said outer beam paths in aselectable one of a plurality of directions inclusive of directionsparallel to, perpendicular to, and diagonal to the direction of saidline sweeps; said additional shifting means comprising second adjustablepermanent magnet means, mounted on the exterior of said tube neck forpositioning on the side of said tube neck region opposite to said oneside in a second location closely adjacent said other of said outer beampaths, for producing a magnetic field intersecting with primaryinfluence said other of said outer beams with a selectable one of aplurality of directions inclusive of directions parallel to,perpendicular to, and diagonal to the direction of said line sweeps; andwherein each of said first and second permanent magnet field producingmeans is independently adjustable.
 2. Beam convergence apparatus for acolor picture tube having a plurality of electron beams emanating fromthe neck of said tube in a nominally common plane and subject to passagetoward the screen of said tube through a region of said neck free of thepresence of internal magnetizable pole piece structures, said apparatuscomprising: two permanent magnet structures mounted for respectivepositioning on opposite sides of said tube neck region for producingrespective fields to primarily influence respectively different ones ofsaid plurality of beams; and means for adjusting the strength andorientation of the field produced by each of said respective magneticstructures, such field orientation adjustments enabling shift of theassociated beam in a selectable one of a plurality of directionsinclusive of a direction parallel to a diagonal of said screen; andwherein: each of said magnet structures includes a pair of magnetizeddiscs of low permeability material coaxially disposed relative to oneanother in a mounting therefor, each disc being magnetized on adiameter, and said discs being rotatable relative to one another to varythe strength of the produced magnetic field.
 3. Beam convergenceapparatus as defined in claim 2, wherein: each of said magnet structuresis rotatable about an axis that is parallel to the longitudinal axis ofsaid tube to vary the orientation of the produced magnetic field. 4.Beam convergence apparatus as defined in claim 3, wherein: saidmagnetized discs are ceramic of barium ferrite material with themagnetization being stronger on one face thereof than on the other, andeach of said magnet structures being assembled with the strongermagnetized faces of said respective discs abutting one another.
 5. Beamconvergence apparatus as defined in claim 4, wherein: said disc mountingincludes a non-magnetic spindle, and said discs are pRovided withcentral transverse holes to snugly fit over said spindle.
 6. Beamconvergence apparatus as defined in claim 5, wherein: said disc mountingalso includes a non-magnetic annular retaining collar having an insidediameter so related to the outside diameter of said disc that the discis firmly secured within the collar.
 7. Beam convergence apparatus asdefined in claim 6, wherein: said disc mounting further includes anon-magnetic plate disposed around the neck of said tube normal to thelongitudinal tube axis, and transverse holes through said plate onopposite sides of said tube neck in said common plane to receive saidrespective disc-supporting spindles.
 8. Beam convergence apparatus asdefined in claim 7, wherein: each of said disc-supporting spindles has aflange at one end to constrain said disc-retaining collars to rotarymovements between said flange and said plate.
 9. Beam convergenceapparatus as defined in claim 8, wherein: said disc-retaining collarshave notched peripheral edges by which to effect said field strength andorientation varying rotations of said discs.
 10. In combination with amultibeam shadow-mask color kinescope having a neck enclosing aplurality of in-line beam sources, said beams passing from said sourcestoward the screen of said kinescope through a region of said neck freeof the presence of magnetizable structures, apparatus comprising: afirst pair of magnetized discs of low permeability material; a secondpair of magnetized discs of low permability material; an apertured mountof non-magnetizable material for said first and second disc pairs, saidtube neck being received within the aperture of said the mount, and saidmount being positioned along the neck axis so as to encircle saidstructure-free region of said neck; and means for rotatably supportingeach of said pair of discs on said mount in respective diametricallyopposed positions spaced from said mount aperture, the discs of eachpair being coaxially disposed and subject to individual rotation aboutan axis substantially parallel to the axis of said neck.